Visual Processing Disorder
Visual Processing Disorder
Visual processing disorder refers to a reduced ability to make sense of information taken in through the eyes. This is different from problems involving sight or sharpness of vision. Difficulties with visual processing affect how visual information is interpreted or processed. A person with visual processing problems may have 20/20 vision but may have difficulties discriminating foreground from background, forms, size, and position in space. The person may be unable to synthesise and analyse visually presented information accurately or fast enough. The eyes look and the brain sees. In this segment the focus is on the visual difficulties associated Learning Difficulties.
The nerve endings at the back of the retina are relayed to the Thalamus by two specialised types of cells:
Parvocellular pathways (small cell bodies) concerned mostly with colour hues and contrast and
Magnocellular pathways (large cell bodies) concerned mostly with movement detection.
Clinical research indicates that in Dyslexia these cell bodies do not differentiate their functions adequately. As a result, many Dyslexics may have a range of visual dysfunctions and/or overlapping of functions between these two pathways. There is growing evidence that dysfunction in magnocellular pathways are responsible for Visual Motion Detection Difficulties in Dyslexics and some forms of Learning Difficulties.
- The white page of a book (background contains all colours and hues) can overwhelm Parvocellularvisual dyslexia symptoms (P) cells and also activate Magnocellular (M) cells by mistake.
- Words can seem to move on the page
- The page of text can appear to be mostly blocks of blurred black (text) with rivers of white running in between.
- The orientation of letters and text may keep changing “d and b” becoming difficult to differentiate and evidenced in letter reversals.
- Using a coloured visual filter (Irlen overlay or spectral filters) can help some people by reducing the colour that may be overwhelming or scrambling the P and/or M pathways.
- Children with Dyslexia can find it difficult to visually track text on a page as this requires fine movement and very tight eye muscle control.
- The cerebellum, a part of the brain that plans our movements a fraction of a second before we execute them, orchestrates this extremely fine motor control. Children with dyslexia often also suffer from dyspraxia (difficulties with fine and/or gross motor control (e.g. awkward gait).
Visual Processing Disorders and Learning Difficulties
Visual processing disorders, which are NOT related to the ability to see clearly, involve difficulties understanding visual information such as movement, spatial relationships, form, or direction. Visual processing disorder is often found with other dysfunctions such as Auditory Processing Disorders, frequently resulting in poor academic performance.
Difficulties can be seen in such school activities as when the young child is asked to identify, or complete a drawing of a human face. This difficulty can be so extreme that even a single missing facial feature (a nose, eye, mouth) could render the face unrecognisable by the child.
The ability to perceive the location of one or more objects in relationship to other objects is a critical skill in reading, math and handwriting. The child, to be successful, must be able to recognise the different symbols, perceive their direction, tell the difference between similar shapes and determine where these are located in relationship to each other. Individuals who have difficulty with spatial relationships may seem unusually clumsy or accident prone may have difficulty reading or may refuse to read, or may have poor handwriting (dysgraphia).
The differentiation of one shape from another or the letter b from d, in othervisual dyslexia symptoms words the ability to perceive the shapes of objects and pictures is an important skill for the developing child to acquire. There is hardly an academic activity that does not require the child to engage in form discrimination. The most obvious classroom activity requiring the child to discriminate forms is that of reading. The learning of the letters of the alphabet, syllables, and words will undoubtedly be impeded if there is difficulty in perceiving the form of the letters, syllables, and words.
Allows us to tell the difference between similar objects, to tell where one object ends and another begins, and to recognise objects and symbols when only part of it can be seen. Individuals who have visual discrimination disorders often mix up letters or numbers and have difficulty reading or scanning pictures for information.
Is a critical part of academic skills. Visual memory allows us to recognise objects and to remember letters, numbers, symbols, words, and pictures. When dysfunction occurs, what is learned on day one, “forgotten” on day two, may be remembered again without difficulty, on day three.
Some individuals have difficulty perceiving or integrating the relationship between an object or symbol in its entirety and the component parts which make it up. Some children may only perceive the pieces, while others are only able to see the whole. Those children that only perceive pieces will have difficulty learning to read and recognising symbols.
Visual Pursuit and Tracking:
The ability to track moving objects while seated or standing, and the ability to keep a stable visual image when the head or eyes are in motion is part of the ocular-vestibular system. Individuals who have visual pursuit disorders have difficulty watching moving objects, difficulty copying from the board, and difficulty reading.
Children at risk for visual processing disorder and other learning difficulties should receive a comprehensive eye examination. This evaluation should be conducted as part of a multidisciplinary approach in which all appropriate areas of visual function are evaluated and managed. This assessment should be further supplemented with an Irlen screening and/or other assessments to clearly identify the intervention required.